Please welcome back Frank Indiviglio for another fascinating species profile.
Perhaps because of its lack of color, the blind cave fish
, Astyanax fasciatus mexicanus
, does not receive nearly the attention it warrants. This 5 inch-long fish was first discovered by Salvador Coronado, a young employee of Mexico’s Department of Fisheries, and it was he who later led a New York Aquarium sponsored expedition to collect the bizarre creatures. The species’ entry into the aquarium world’s consciousness is recounted by expedition member William Bridges, of the Bronx Zoo, in his initial report – “…at three o’clock on a March afternoon, a thousand feet inside the cave, two of us dragged a net out of the black water and revealed a dozen little flopping white fish…”. Amazingly, fish from that first collection appeared in three distinct forms – with normal eyes, with eyes of reduced size and without eyes. Fortunately for we fish enthusiasts, captive-born blind cave fish eventually found their way into the pet trade.
The blind cave fish is found in only one cave, La Cueva Chica (the “Little Cave” – the entrance is only 15 feet wide) near Pujal, in San Lois Potosi, Mexico (related species have since been found in other caves). This fact alone should grant it special status among fish keepers, but there is much more to distinguish it – including a rare glimpse at fish adaptation in progress. Apparently, fish with normally developed eyes live in a nearby river, the Rio Tampaon, and are regularly swept into the cave by the current. There, deprived of light and the need for sight, the eyes degenerate. As time goes on, their descendents are born with gradually more reduced eyes, until the eyeless form emerges. Although I have not read evidence of it, I imagine that inter-breeding with eyeless fish already in the cave may hasten the process.
Fish in pools nearest the cave’s entrance rely upon flies, spiders and other invertebrates for food, while those deep inside subsist upon bat guano, dead bats and, I would venture a guess, fleas and other invertebrates that fall from the bats’ fur.
Check back on Friday to read the rest of this article.
I kept a few of these before…might want to get them again as they were quite interesting. Do you know how such an unusual fish crossed from the zoo to hobby sector? Can all fish in the hobby be considered descended from the original collection for this cave, or were their any subsequent collections? Also some people have mentioned many blind caves now have more silvery sides than they used to and otherwise are changing due to breeding on fish farms. thoughts?
Frank Indiviglio here. Thanks for your question and my compliments on your wide interests – rare today, and refreshing.
Well, you certainly have posed an interesting question. The blind cave fishes in the pet trade truly do represent a remarkable situation – a fish that is at once a natural rarity, being limited to a stream within a single cave, and a popular pet. The only parallel I can draw is, oddly enough, to another denizen of Mexican waters – the Mexican axolotl, Ambystoma mexicanum. This salamander is limited in distribution to 2 lakes, and is nearly extinct in the wild (Lake Chalco has been drained and Lake Xochimilco has been receiving waste water from Mexico City for over 100 years), yet is an important laboratory animal and widely-bred by hobbyists.
I’ve found that older publications such as Exotic Aquarium Fishes (Innes, 1938. Metaframe Corp: Maplewood) are good starting points when looking for background information. In this case my hunch proved correct – upon checking my copy of this book, I learned that the author, William T. Innes, actually described (taxonomically, for the first time) the fish in question in 1936 (along with Carl Hubbs).
To quote from Exotic Aquarium Fishes: “In 1936 Mr. Basil Jordan, at Dallas, Texas, sent the author the eyeless fish from which the above photographic illustration was made….it was found to be a new species, no doubt descended from Astyanax mexicanus (the Mexican tetra)”. The author goes on to describe the various collecting expeditions that followed. Most ichthyologists continue to consider this fish to be a distinct species, while others label it a subspecies of the Mexican tetra on the grounds that progeny of crosses with the nominate species are fertile.
The blind cave fish’s entry into the trade appears to have occurred not long after its discovery, as collection was largely unregulated for a time. Additional populations of what appear to be the same or a very similar tetra have since been unearthed in the general area of the original collection site, and these may have found their way into the trade as well. An amusing quote from a later edition of Mr. Innes’ book: “(the blind cave fish)…seldom bumps into anything (never hard). Most aquarists at first feel a needless pity for it, but they end by regarding it as a special pet”.
As for their developing a silvery color on fish farms, that seems to be a move towards the original, colored form (the cave fishes are white) and in line with other quirks in cave fish genetics/development. Blind cave fish mated to sighted fish produce fry with eyes having varying degrees of development and sight. Fry with two blind parents begin to develop eyes as embryos, but these degenerate quickly. Recent studies have shown that young blind cave fish can detect light via the pineal gland, but that this ability declines rapidly….all told, the blind cave fish seems to be in the process of evolving, and many have suggested that the split from the parent species occurred quite recently.
Thanks again for your interest.